I. Field of the Invention
The present invention relates generally to landing gear construction for small aircraft. More particularly, my invention relates to a tail wheel assembly for small aircraft that secures the tail wheel and eliminates jarring or jerking, and other unwanted vibration, thereby preventing tail wheel shimmying.
II. Description of the Prior Art
In general, the concept of stability relates to the characteristics of an aircraft in maintaining its course and direction. In flight, the term "stability" is often equated with the ability of the plane to fly itself. Stability can either be static or dynamic. Static stability involves only the return of the disturbed object to its original position. This was the goal of the early airplane designers; that the airplane would try to return to its original orientation (position) after a disturbance, such as a gust of wind. Dynamic stability is concerned with how much time it may take for the object to return to its original position. If the plane eventually returns to its original position, then the system is considered dynamically stable. If it does not, then it is considered dynamically unstable.
The concept of "control" is a science relating to the human experience in flying and handling a given aircraft. The concepts are related, because when "control" is optimized, a given airplane will be relatively easy for the pilot to fly, and highly stable in flight. The small airplanes used at local airports are very stable; they are good for both beginning pilots and the more experienced pilots. They are very easy to fly and very forgiving of pilot mistakes. Although usually discussed as flight characteristic, stability and control are equally important during takeoff and landing.
When the plane is in contact with the runway, sudden movements to the left or right of the landing surface are disfavored. Stability dictates that the plane move forwardly and decelerate smoothly during a landing without sudden "jerkiness." Similarly, as a plane taking off leaves the runway and breaks contact with the ground, irregular movements caused by runway-contact can affect flight path stability. One significant cause of vibration and jerkiness during takeoffs and landings is the tail wheel assembly, that can vibrate deleteriously when I contact with the runway.
While on the ground, static stability is enhanced by the normal three-point wheels of the aircraft. Usually a single tail wheel assembly at the aircraft rear completes the "third point" necessary for establishing a stable, planar position. With older small planes having "fixed" tail skid assemblies, the tail skid may be permanently oriented in a position parallel with the longitudinal axis of the airframe. In some tail wheel mounting designs, upward or downward movements of the tail wheel are enabled. However, if the tail wheels are mounted too loosely, they will shimmy or vibrate during takeoffs and landings. On the other hand, if they are secured too rigidly, and cannot "give" in response to runway contact, proper handling can be negatively affected during landings. The time periods just before liftoff, and during landings, are often critical, and yet conventional tail wheel mounting assemblies allow the reartovibrate.
The latter problem can be particular vexatious when operating agri-chemical dispensing airplanes from dirt runways. When the plane takes off, it is full of fuel and agrichemical, at maximum weight. Jolts or jerking motions imparted by vibrating tail wheel assemblies during takeoffs can be disconcerting, to say the least. When the plane returns for a landing, it is much lighter, and flight characteristics are different than they were immediately after takeoff. During a landing, when the tail wheel makes first contact with the landing surface, a "smooth" and non-jerky transition is desirable. In the fraction of a second that the plane is neither fully airborne nor fully landed, the path of least resistance for wheel movement may not be straight down the runway. In other words, because of wind gusts and numerous other variables, a sleight movement in tail wheel orientation from "true straightness" can decrease stability.
In other words, during takeoffs and landings especially, conventional tail wheel assemblies vibrate, rattle, and shimmy. If the tail wheel assembly is modified to prevent vibration, it must nevertheless be able to "give" slightly when contacting the ground.